Painting - Exterior metal doors

Any suggestions you have for painting around the big, oval window on my front door without leaving noticeable brush marks would be appreciated. Not being a pro, would I be better off not using the electric sprayer I have (and have never used) and trying to do this with brushes and/or rollers? This will be the first coat of primer and paint for this door.
Thanks.

I always use brush and rollers, its what I'm comfortable with. I assume the door is pre primed from the factory, but I usually prime it anyways. Use a good quality exterior latex primer and paint. I would suggest semi-gloss for a door. Use the roll on/lay off method. Roll the paint on fairly thick to one section of the door, but not so thick its running. Then use the brush to gently stroke it out, helping it level itself. This will minimize brush strokes. And don't do it in the direct sunlight, it will dry faster than you can paint it.

Thanks for the reply, pro.
Because I have to replace the weatherstripping on the bottom of the door, I was going to take it off the hinges, then paint it while I had it off. Should I lay it flat or keep it upright when painting it? Also, when "laying off" should I use just enough pressure to level out the paint, or more than that? You're right-it does have factory primer on it, but the builder never painted it after installing it. I figured I'd sand the surface some before priming...is that a good idea?
Thanks again.

Just a light sanding, use 150 or 220 grit, then use a tack cloth to remove the dust. Taking it down is a good way to paint it, remove the door handle too. I paint them standing up, but laying down would be fine, just make sure the paint isn't too thick and it pools up in the low places. Standing up, I know right away if its too heavy, cause it will sag and run. When laying off, I use a 'loaded' brush thats wiped clean of excess paint. A dry brush will suck the paint back off the door. A loaded brush means dipped in the paint and allowed to soak up paint, then scraped off on the rim of the can. Just gently drag the brush across the surface just enough to remove the roller stipple, and not hard enough to move alot of the paint around.